- 學位論文
具有顯著飽和區之垂直有機電晶體
Vertical Organic Transistors with Pronounced Saturation Regions
摘要
摘要 在這本論文中，將探討垂直式有機電晶體中的有機材料層替換。以pentacene為基底的水平式和垂直式有機電晶體將被討論。因為通道長度和材料低遷移率(mobility)的限制下，導致以源極/汲極上方接觸(top contact)的水平式有機電晶體出現高操作電壓。藉由減小通道長度，具有加強電洞注入的LiF層厚度和薄基極金屬厚度，垂直式的有機電晶體並存著有小於5伏特的驅動電壓和電流開關比大於102的特性 。由於元件在電流調制狀況下觀察到基極再結合(recombination)現象的增加，使得在共射極模式下觀察到較小的電流增益。雖然以pentacene為基底的高電流增益有機電晶體已經成功地被製造，但是在大氣環境下元件的穩定度仍然是個爭議。基於理解這項原因，具有相同結構以CuPc為基底的三極體發展不但可以證明元件結構是可以適用於替換各種有機材料而且改善元件的穩定度。因此，以CuPc為基底具有薄基極金屬可操作在飽和區的有機垂直式三極體可被研究。 用最佳化厚度0.4nm的LiF，元件在基極電流密度為-2.5 mA/cm2 和射極-汲極電壓為-5 V下，共射極電流增益為3.63可以被觀察到。在傳輸常數(α)趨近於1下，在共射極模式下被觀察到的小電流是因為非均勻電流導致電流減少。以CuPc為基底的元件和pentacene為基底的垂直式三極體比較下，由於CuPc 的電洞遷移率較低，所以其共射極電流增益也較小。架設一個用兩個以CuPc基底的Schottky二極體背對背(back-to-back) 具有不同基極金屬厚度的垂直式有機三極體特性，可以更一步研究薄鋁厚度對元件效果的影響。在輸出電流電壓特性下，垂直有機三極體存在一個平坦的飽和區。隨著基極鋁厚度增加而共射極的電流增益變小是因為在鋁金屬上開口孔洞減少導致在基極再結合(recombination)電流增加所造成。當汲極-射極電壓為-5V和基極電流密度為2.5 mA/cm2，元件鋁厚度為4.5nm，共射極的電流增益可達到1.9。
並列摘要
In this thesis, vertical organic transistors with alternate organic materials are investigated. Pentacene-based planar- and vertical-type organic thin film transistors (OTFTs) are investigated. High operation voltages are observed for the planar-type OTFTs with top source/drain electrodes, which results from the limitations of channel length and low material mobility. With a reduced channel length, a LiF hole-injection enhancement layer and a thin metal gate, the vertical-type pentacene OTFTs exhibit a low voltage operation of less than 5 V and a compatible on/off ratio of larger than 102. The smaller current gain observed from the device under current modulation is attributed to the increase of base recombination current under the common-emitter mode. Although pentacene-based vertical organic transistors with high current gain are successfully fabricated, the reliability of the devices under atmospheric ambient condition is still an issue. Based on the understandings, the development of CuPc-based triodes with similar device structures would not only prove the device structures suitable for alternate organic materials but also improve device reliability. Therefore, CuPc-based vertical organic triodes with thin metal base operation under saturation region are investigated. With an optimized LiF thickness of 0.4 nm, a common-emitter current gain of 3.63 is obtained for the device at JB = -2.5 mA/cm2 and VCE = -5 V. With a close-to-unity transport factor, the observed smaller current gain is attributed to the decrease of emitter current resulted from the non-uniform current flow under the common-emitter mode. Compared with pentacene-based vertical triodes, the CuPc-based devices exhibit a smaller common-emitter current gain resulted from its lower hole mobility. To futher investigate the influence of Al film thickness on the device performances, the characteristics of vertical organic triodes fabricated by using two copper phthalocyanine (CuPc) back-to-back Schottky diodes with different metal base thicknesses are fabricated. The vertical organic triodes exhibit pronounced saturation regions in the output current-voltage characteristics. The common-emitter current gain reduces with increasing the Al base thickness due to the increase of recombination current at the base end resulted from the reduction of opening voids in the Al metal film. The common-emitter current gain of the device with 4.5 nm thick Al base reaches 1.9 at VCE = –6 V and JB =2.5 mA/cm2.